This invention relates to methods of stabilizing silicone hydrogels against hydrolytic degradation.
Contact lenses have been used commercially to improve vision since at least the 1950s. The first contact lenses were made of hard materials and as such were somewhat uncomfortable to users. Modern lenses have been developed that are made of softer materials, typically hydrogels and particularly silicone hydrogels. Hydrogels are water-swollen polymer networks that have high oxygen permeability and provide good comfort to lens users. These materials have enabled many more patients to wear lenses due to their increased comfort. Despite the advantages of these lenses to patients, the same lenses present unique problems to the manufactures of those lenses.
Contact lenses, like other medical devices, are stored in aqueous solutions. The mechanical properties of silicone hydrogel contact lenses degrade over time when lenses are stored at ambient or elevated temperature in aqueous solutions. This degradation, shortens the shelf life of a silicone hydrogel and can be quantified by measuring the increase in tensile modulus. Therefore, there is a need to find a method of increasing the stability of silicone hydrogel contact lenses in aqueous solutions. It is this need that this invention fills.